334 HEAD AND NECK 



Oculo-motor (3rd cerebral). 

 Trochlear (4th cerebral). 

 Abducent (6th cerebral). 



Nerves, . ,-| j a ', I from ophthalmic division of the trigeminal 

 acrima , x Qr ^^ cere ^ ra j nerve> 



Zygomatic branch of the maxillary division of the tri- 

 geminal nerve. 



"/-"! I' 



Ciliary ganglion. 

 Lacrimal gland. 

 Fascia Bulbi. 



Dissection. The roof of the orbit must be removed with the aid of the 

 saw, the chisel, and the bone forceps. Begin by removing the thick cranial 

 wall above the orbital opening, leaving only a thin portion corre- 

 sponding to the superior orbital arch. Whilst this is being done, 

 care should be taken to preserve the soft parts of the forehead and the 

 upper eyelid. It is of great advantage to retain, throughout the whole 

 examination of the orbital cavity, the bony ring which constitutes its opening 

 on the face. The thin roof of the orbit may next be removed with the 

 chisel and bone forceps. The lesser wing of the sphenoid, where it forms 

 the upper boundary of the superior orbital fissure, should be taken away 

 by the bone forceps, but the dissector should carefully preserve intact the 

 ring of bone around the optic foramen. The superior orbital fissure is 

 now fully opened up, and the various nerves, as they enter the orbit from 

 the cavernous sinus, may be followed out. Lastly, the anterior clinoid 

 process may be taken away with advantage. 



Periosteum. If the dissection has been successfully 

 carried out, the periosteum clothing the under surface of the 

 orbital roof will be exposed uninjured. The periosteum of 

 the orbit forms a funnel-shaped sheath, which encloses all the 

 contents of the cavity except the zygomatic nerve, and is but 

 loosely attached to its bony walls. Posteriorly it is directly 

 continuous, through the superior orbital fissure, with the 

 dura mater. Expanding with the cavity, it becomes con- 

 tinuous anteriorly, around the orbital opening, with the 

 periosteum which clothes the exterior of the skull. Here 

 also it presents important connections with the palpebral 

 fascia. 



Reflection of the Periosteum and the subsequent Dissection. The 



periosteum should be divided along the middle line of the orbit, and then 

 transversely close to the orbital opening. It can now be thrown medially 

 and laterally. When this is done, the lacrimal gland will be exposed in the 

 antero-lateral part of the cavity. Further, the large frontal nerve, lying 

 upon the upper surface of the levator palpebne superioris, will be seen in the 

 middle line of the orbit ; as it approaches the anterior part of the cavity 

 it is joined by the supra-orbital artery. The other superficial structures 

 are usually more or less obscured by the soft pliable fat, which every- 

 where fills up the interstices between the different orbital contents. On 

 carefully separating this, along the medial wall of the orbit, the superior 

 oblique muscle will be more fully displayed, and lying upon and entering 



